23-Ind-B5 Ergonomics · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — Dec. 2018 — 17-Ind-B5 Ergonomics. Three-hour, open-book exam (any non-communicating calculator permitted); NIOSH lifting tables (Appendix 1) and a manual-materials-handling assist-device table (Appendix 2) are supplied on the exam's own pages. The paper's instructions state a total of four questions: Part A (Questions 1–2) is mandatory, Part B asks the candidate to choose one of Questions 3 or 4. All four questions are solved below.
Reference texts: Sanders & McCormick, Human Factors in Engineering and Design (7th ed.) — environmental ergonomics, human-factors analysis methods, error taxonomy (Reason's model), and controls/displays population-stereotype/spatial-compatibility principles (incl. the classic Chapanis & Lindenbaum stove-burner control-panel study); Waters, Putz-Anderson & Garg, NIOSH Applications Manual for the Revised NIOSH Lifting Equation (1994) — the RWL/LI formula and multiplier tables reproduced on the exam's own Appendix 1; NIOSH, Elements of Ergonomics Programs (1997) and CSA Z1004 (Canada) — workplace musculoskeletal-disorder (MSD) prevention programs; CSA Z1002 — hazard identification, elimination and risk assessment.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Both layouts share the same underlying flaw before their specific knob orderings are even considered: a 2×2 spatial arrangement of burners is being controlled by a 1×4 linear row of knobs, which forces an arbitrary mapping between a two-dimensional layout and a one-dimensional control set – this is precisely the control/display spatial (population-stereotype) compatibility problem documented in the classic Chapanis & Lindenbaum stove-panel study: whenever knob geometry does not directly mirror burner geometry, users must consciously translate rather than react automatically, and selection errors (reaching for the wrong burner's knob) rise measurably, with the associated risk of activating an unintended burner – a burn/fire hazard, not merely an inconvenience.
The left layout (C, A, B, D) is the worse of the two: reading left to right, the knob order visits bottom-left, top-left, top-right, bottom-right – it does not correspond to any natural reading order (not row-by-row, not column-by-column), so there is no consistent rule a user can apply, and every selection effectively requires memorization or a label check. The right layout (A, C, B, D) is a partial improvement – the first two knobs (A, C) are the left-column pair and the last two (B, D) are the right-column pair, giving a column-grouped structure – but front burner C is still placed second rather than adjacent to its natural left-right neighbour in an intuitive front/back sense, so a user can still expect knob position 2 to control the front-left burner by a row-reading habit and instead activate the rear-left one. Neither layout achieves true spatial compatibility (each knob positioned so its relative location in the row matches its burner's relative location in the grid), and both increase the risk of an inspection/situation-assessment-stage mistake (wrong burner activated because the wrong item was selected, not because the knob itself was operated incorrectly) – in Reason's terms from Question 3, a rule-based or knowledge-based selection mistake rather than a slip.
Three alternative solutions, in order of preference:
Solution 1 (preferred) — matched spatial (staggered) knob layout. Arrange the four knobs in the same relative 2×2 spatial pattern as the burners (e.g. two knobs set slightly back for the rear burners and two set forward for the front burners, or knobs physically staggered left/right to mirror the grid) so the control panel is a scaled-down mirror of the cooktop – this achieves genuine population-stereotype compatibility and needs no learning or label-reading at all.
Solution 2 — individual knob mounted beside/below its own burner. Eliminate the row-of-four panel entirely and place each knob directly adjacent to (in front of) the burner it controls, on the front bezel closest to that burner – the strongest possible spatial mapping, at the cost of higher manufacturing complexity (four separate control locations instead of one panel) and reduced clearance for a single hand to reach a rear knob without passing over a front (potentially hot) burner.
Solution 3 — retain the linear row, add colour/shape coding. If the panel-manufacturing tooling cannot change, colour-code and shape-code each knob to match a corresponding marking at its burner (e.g. a red ring around both burner D and its knob) – a lower-cost fix that reduces, but does not eliminate, the mapping problem, since it still requires the user to look and match rather than react spatially.
Cost. Solution 1 (staggered, spatially-matched knob panel) requires new control-panel tooling and a revised front-bezel stamping/moulding die – a one-time non-recurring engineering (NRE) cost, illustratively on the order of $150,000–$250,000 for tooling plus design validation for a single stove product line, with negligible ongoing per-unit cost difference versus the current linear panel (same number of knobs, same wiring/gas-valve count, only their physical arrangement changes).
Benefit. The Chapanis & Lindenbaum-class literature on this exact control/display problem reports markedly fewer burner-selection errors with a spatially matched panel versus a linear row – a meaningful reduction in wrong-burner activation. For a manufacturer, this translates into (1) fewer burn-injury liability claims and the associated legal/settlement/insurance-premium cost, (2) fewer product-safety complaints and reduced recall exposure, and (3) a marketable safety differentiator. Even a conservative estimate – avoiding a handful of liability claims per year at a typical settlement/legal cost in the tens of thousands of dollars each – recovers the one-time tooling cost within a few years of production at typical stove sales volumes, before counting the harder-to-quantify brand and recall-avoidance benefit.
Conclusion. The tooling cost is a one-time, bounded NRE expense, while the benefit (injury/liability avoidance) accrues every year the redesigned panel is in production across the full unit volume – the cost-benefit case favours adopting Solution 1 for any reasonably high-volume stove line, with Solution 3 (colour/shape coding) as a lower-cost interim fix only where tooling change is not immediately feasible.
